Metal parts for clothing ornament such as hooks, buttons, pant hooks and eyes, spring hooks and so on are manufactured through complicated working steps such as pressing, coining and the like because designing properties (designability and fashionability) are required to be provided for the purpose of distinguishing over other products in addition to the functionality. Therefore, metal materials as a raw material for these parts are required to have a plastic workability durable to severer working, and soft materials such as brass, aluminum alloys and the like are frequently used since early times. Also, joining between mutual parts or fixing to the cloth is generally conducted by “caulking” through pressing, from which it is also required to use a soft material.
Recently, severer inspections are carried out by adopting a needle detecting device for judging whether or not a fractured needle remains in a product during sewing through presence or absence of magnetic property from a viewpoint of attaching importance to safety. Since these inspections are conducted in final products, they are carried out after the attachment of metal parts such as hooks, buttons, pant hooks and eyes and so on. In this connection, metal parts made from the aforementioned brass, aluminum alloy and the like are small in the magnetic property and are not falsely detected as a fractured needle, so that they do not particularly pose a problem for the inspection.
In the metal parts made from the brass, aluminum alloy and the like, however, there may be caused an inconvenience that discoloration is brought by chemicals such as dyestuff or the like remaining in a cloth on the way of transferring at a vinyl-packed state. Consequently, it is examined to change them into a metallic material causing no discoloration, for example, stainless steel or the like. In JP-A-H08-269639, for example, there is a proposal that Ni—Cr based nonmagnetic stainless steel is applied to metal parts for clothing ornament requiring spring properties while utilizing high strength as a characteristic of the stainless steel as compared with the brass or aluminum alloy.
However, the Ni—Cr based nonmagnetic stainless steel of JP-A-H08-269639 has a magnetic permeability of about 1.005 though it is said to be nonmagnetic, so that the nonmagnetic property is insufficient, and when it is applied to pant hooks and eyes or socket having a large weight, false detection may be caused by the detecting device. Also, such a stainless steel can not be said to be good in the plastic workability because the strength is enhanced by cold rolling and further the steel is hard even after the solid solution heat treatment for imparting the spring property. As regards the caulking, there is a problem that it is difficult to fix to the cloth by a common process. In order to use the stainless steel instead of the brass or aluminum alloy, therefore, it is required to further improve the nonmagnetic properties and the plastic workability (softening).
In JP-A-2005-154890 are proposed Mn—Cr based austenitic stainless steels for press forming such as deep drawing or the like as a nonmagnetic stainless steel improving the workability. In this stainless steel, however, the chemical composition, stability of austenite phase, production indications such as stacking fault energy and the like are designed to be controlled so as to maintain the nonmagnetic property even after the plastic working, but the magnetic permeability after the resulting material is subjected to cold rolling at 60% is about 1.01-1.05, so that the nonmagnetic property is insufficient.